You may have to use the console to get out of the room and talk to the NCR interrogator to finish the quest.
Simplest solution would be to use the command "tcl" to walk through the wall and talk to her. (Hit "~" to bring up the command console and type "tcl" then enter). To turn clipping back on just repeat that.
If that doesn't work then while you're out there, bring up the command console and :
1) Click on her - her name should appear in white letters towards the top of the screen.
2) Write down the numbers and letters that appear to the right of her name (may need them if this does not work)
3) while she is "selected" type "disable" and hit enter then immediately type "enable" and hit enter.
4) Try talking to her again.
If THAT doesn't work then go back in the cell and -
1) Type "prid XXXXXXX" where the x's are the number I told you to write down.
2) Type moveto player
3) Try the disable+enable command sequence again.
Good luck- but those stopes usually succeed in unsticking npcs. Really just walking through the wall will probably work though.